1. Field of the Invention
This invention relates to disc cartridges for accommodating recording discs capable of having information recorded thereon and read out by an appropriate reading apparatus. More particularly, the invention relates to a disc cartridge comprising a casing designed to accomodate the disc and to allow the read-out and/or the recording of information while the disc is housed in said casing. The recording discs concerned may be of the type generally designed as "compact disc" or "CD", and more particularly information carrying discs called "CD ROM", although the invention is in no way limited to this type of disc.
2. Related Art
Disc casings of the type referred to herein are being produced by various manufacturers according to a similar basic design in order to be usable in standardized reading apparatus, in which the disc is read while housed in the casing. Such known disc casings, also called cartridges, generally comprise a lower casing element designed to accomodate the disc, the bottom of this element comprising an opening, a first part of which is designed to provide a passage for a shaft for driving the disc in rotation, this shaft belonging to a disc-reading apparatus, and a second part of which is designed to provide access for a disc-reading device belonging to the same apparatus. The lower casing element is usually closed by a casing cover constructed in such a manner as to make possible the closing or the opening of the casing and provide a plane wall facing the bottom of the lower casing element.
According to a known casing design, a movable shutter is provided on the casing for closing the opening in the bottom of the lower casing element to protect the disc against risk of mechanical damage and to limit the penetration of dust inside the casing when the disc is not used in the reading apparatus. This shutter is provided with a mechanical device for ensuring its automatic retraction and disengagement from said opening when the casing is introduced into the reading apparatus, and for ensuring its return to its closing position when the casing is withdrawn from the reading apparatus. Such a device generally includes actuating levers and at least one spring and is therefore relatively complicated, fragile and expensive. Hence the manufacturing cost of such a disc casing is rather high and there is further a non negligible risk of defective functioning, in particular when the casing reaches a more or less advanced state of wear.
Prior art disc casings are usually provided with a disc clamping element comprising generally a circular part of a plastic material in which is housed a plate made of a magnetic material, this clamping element being designed to be attracted towards the surface of a frontal magnetized end of the driving shaft for rotating the disc, thereby ensuring the locking of the disc with this shaft. This clamping element is retained in a housing arranged in the cover of the casing opposite the bottom of the lower casing element, in such a manner as to provide for free rotation of this element in relation to the casing when the same is placed inside the reading apparatus and the driving shaft is locked with the disc. The presence of such a clamping element as a part of the disc casing also leads to increased costs for such a type of casing.
In the prior art casings, a further major drawback results from a certain freedom of the disc to move within the casing when the same is not inserted in a reading or recording apparatus, in particular during transportation. Such a movement of the disc inside the casing produces frictional wear resulting in fine particles which can come to lie on the surface of the disc and create perturbations in the reading or recording process. In the case of recordable discs, currently designated as CDR:s, it is particularly important that the surface of the disc remains free form dust or other contaminations before the disc is being recorded, which is not assured when the disc is housed in a prior art casing where it can move inside its compartment.